Re: [PATCH] x86/oprof: fix !HVM && !PV32 build

[Andrew Cooper <andrew.cooper3@citrix.com>]

On 16/04/2021 09:16, Jan Beulich wrote:
> clang, at the very least, doesn't like unused inline functions, unless
> their definitions live in a header.
>
> Fixes: d23d792478 ("x86: avoid building COMPAT code when !HVM && !PV32")
> Reported-by: Andrew Cooper <andrew.cooper3@citrix.com>
> Signed-off-by: Jan Beulich <jbeulich@suse.com>

I agree this will fix the build.  However, looking at the code, I'm not
sure the original CONFIG_COMPAT was correct.  In particular, ...

>
> --- a/xen/arch/x86/oprofile/backtrace.c
> +++ b/xen/arch/x86/oprofile/backtrace.c
> @@ -43,6 +43,7 @@ dump_hypervisor_backtrace(struct vcpu *v
>      return head->ebp;
>  }
>  
> +#ifdef CONFIG_COMPAT
>  static inline int is_32bit_vcpu(struct vcpu *vcpu)
>  {
>      if (is_hvm_vcpu(vcpu))

... this chunk of logic demonstrates that what oprofile is doing isn't
related to the Xen ABI in the slightest.

I think OProfile is misusing the guest handle infrastructure, and
shouldn't be using it for this task.

~Andrew

> @@ -50,6 +51,7 @@ static inline int is_32bit_vcpu(struct v
>      else
>          return is_pv_32bit_vcpu(vcpu);
>  }
> +#endif